1. Field of the Invention
The present invention relates to a Ni-Cr-W superalloy that simultaneously satisfies the requirements for high-temperature strength, corrosion resistance, good producibility, good hot workability and resistance to embrittlement due to thermal aging and which hence is particularly suitable for use as the high-temperature structural material of high-temperature gas-cooled reactors.
2. Prior Art
Several N1--Cr--W, Ni--Cr--Fe--Mo and Ni--Cr--W--Mo base alloys have been developed for use as high-temperature structural materials of high-temperature gas-cooled reactors and alloys are known by various names such as N1--Cr--W alloys, Ni-base superalloys, forgeable Ni-base superalloys, heat-resistant alloys for welding structures and high-temperature corrosion-resistant Ni-base alloys. None of the alloys, however, has been proposed so far simultaneously satisfy the requirements for high-temperature strength and corrosion resistance (the term "corrosion resistance" as used herein means not only resistance to corrosion in a strongly oxidative atmosphere such as air atmosphere but also resistance to corrosion in a weakly oxidative atmosphere such as helium containing trace impurities as exemplified by the primary coolant used in high-temperature gas-cooled reactors), and many prior art alloys achieve high-temperature strength at the sacrifice of corrosion resistance (in particular, resistance to corrosion in helium). On the other hand, alloys having superior corrosion resistance are poor In the high-temperature strength characteristic.